Yes it'll handle it fine

No, to many miles....too risky

Has anyone blown up their 4.6L 2 valve combo while running 8psi? If so what was the cause of the failure? Reason I’m asking is I’m wanting to get a 99-04 and run 8 lbs. until I can afford a forged bottom end. But this engine will most likely be a high mileage engine like over 80,000 miles. If it passes a cylinder leakdown test and compression test, it should be ok to handle the power as long as I don’t over rev the engine correct? Combo will be pretty simple to start with, basically a stock GT w/ procharger (Intercooled), injectors, Kenne Bell Boost - A – Pump, 4R70W, and a custom (Conservative) tune on a dyno. Not to be revved past 6k rpm. I know the stock Trans may not hold up but that’s cheaper and easier to replace / rebuild than a motor. So with that much mileage should I be concerned about the engine having 8psi and around 360 rwhp? Assuming it passes the cylinder leakdown and compression tests?

I put a blower on my car at 90k miles. Ran perfectly fine for 30k more miles on 7-8 pounds of boost until some detonation took out a piston. Typically at 450ish rwhp, the rods start breaking. At ANY horsepower level, any significant amount of detonation will break the top ring lands. So whatever you do, make sure the tune is spot on, and NEVER keep your foot in the throttle if you ever hear at detonation. There are other failures, too, like the oil pump going bad or timing chains breaking, but those could happen on a completely stock car.

Bottom line: get a good tune, keep it under 6k rpm, and it'll live for quite a while on 8 pounds of boost.

Also, get a transmission cooler and do the J-mod, and the transmission will be perfectly fine at that level.

Founding Member

Right, there isn't anything specific about a higher mileage engine that makes it less tolerant too boost. ANY engine will experience a failure if you get into detonation for an extended period. Like sneaky said, it's all in the tune.
On my 2.3, I had a vacuum line blow off the fuel pressure regulator. That caused the fuel pressure to drop, and detonation took out the rings on a cylinder. I guess you don't have to worry about that with a 98+ since they don't have a fpr.
Anyway, these engines tolerate mileage very well. My GT has 218k and is still very strong. Only issues you might run into are valve stem seals and chain guides, both of which aren't a big deal to replace. If you want the engine to last indefinitely with a blower, it might be better to keep it at or under 400-425 rwhp and 6k.

I put my ProCharger on at 95k. Its a stage 2 kit that was supposed to run between 9 and 10 psi of boost with ProChargers bigger intercooler. I really don't know how many psi it was making but it hasn't given me any trouble. I told my tuner to make it safe.

I just opened up the exhaust, got a bigger throttle body and plenum, installed a fuel pump booster. Just put on a smaller pulley. Going to the same tuner and will tell him the same thing.

Don't be afraid of intercooled 8 psi. Make sure you have a good tuner and specify that you don't want the car tuned right up on the ragged edge.

My biggest concern would be oiling system. That's I believe how my motor got tore up. I haven't taken it out of the car yet so I don't know exactly what failed. If it's tuned right I was told 450 is teetering with disaster. And I tipped on the wrong side of the scale I guess lol. With thst many miles I would consider a new oil pump and check or upgrade the sump. Just my 2 cents